Scheil Advanced Options: Property Models

This topic has advanced settings information for the Show advanced Scheil options checkbox that is available for a Property Model Configuration windows. The main settings are on the Configuration tab.

These settings are based on the Scheil Calculator settings with minor differences in wording or application. See Scheil Calculator: Advanced Options.

For theory or background details about Scheil, start by reviewing Scheil-Gulliver Solidification Calculations.

To view all of these settings, click the Show advanced Scheil options checkbox.

Enter a Temperature step during Scheil for the Scheil simulation. Temperature step is given in the same unit as the temperature in the Condition Definitions.

Global minimization is enabled by default i.e. the Global minimization checkbox is selected.

It is recommended to keep global minimization on as it makes the calculation more accurate. However, turn it off if you find that the calculation is taking too long for any particular system, and accuracy is not the highest priority.

For this setting, a global equilibrium test is performed at selected intervals when an equilibrium is reached. By default it is at every 10 th Scheil step but this can be changed using the Global test interval setting. The global equilibrium test is also done every time the set of stable phases tries to change. This costs more computer time but the calculations are more robust.

Use the Global test interval setting to change the interval at which a global equilibrium test is done, which by default is every 10th step as long as there are no changes in the set of stable phases. Every time the set of stable phases tries to change, a global equilibrium test is also done regardless of the test interval value chosen. A global equilibrium test means that the calculated equilibrium state obtained by the ordinary minimization calculation is tested against the Global Minimization Technique, and if the result is found unstable then the full global minimization calculation is performed instead.

The default in the list is the LIQUID phase already defined in the chosen database.

Enter a value for the Solid fraction for evaluating liquidus temperature. A small fraction larger than zero can be used to avoid small amounts of high temperature stable phases for the evaluation of liquidus temperature.

Enter a value in the field for Terminate at fraction of liquid phase amount.

For Crack Susceptibility Coefficient model, the value should not be larger than the setting Liquid fraction: Smallest for vulnerability.

Enter or choose a value for the Max no. of iterations. By default, the program tries 500 iterations before it gives up. As some models give computation times of more than 1 CPU second/iteration, this number is also used to check the CPU time and the calculation stops if 500 CPU seconds/iterations are used.

The default Required accuracy is 1.0E-6. This is a relative accuracy, and the program requires that the relative difference in each variable must be lower than this value before it has converged. A larger value normally means fewer iterations but less accurate solutions. The value should be at least one order of magnitude larger than the machine precision.

The default Smallest fraction (or Smallest fraction in a phase for Property Models) is 1.0E-12. This is the value assigned to constituents that are unstable. It is normally only in the gas phase you can find such low fractions.

The default value for the smallest site-fractions is 1E-12 for all phases except for IDEAL phase with one sublattice site (such as the GAS mixture phase in many databases) for which the default value is always as 1E-30.

The default Smallest fraction for alloy composition is 1.0E-7. A smallest value assigned to alloy mole/mass fraction in case a smaller input value for an element is entered.

The Approximate driving force for metastable phases checkbox is selected by default. Click to clear the checkbox to change the default as required and based on the options described below.

This setting involves the convergence of metastable phases and affects their driving forces. It can also have an effect on when an equilibrium is considered successful.

The default is to allow an equilibrium with metastable phases that have not converged, as long as the stable phases have converged. This is efficient but often causes approximate values of the driving forces for the metastable phases.

If you change the default, it enforces metastable phases to converge. This gives accurate driving forces for metastable phases as well as stable phases. It can however take a slightly longer time, and if metastable phases do not converge it causes the equilibrium calculation to fail.